Date: Mon, 10 Mar 2003 19:22:38 +0100 From: "Poul-Henning Kamp" <phk@phk.freebsd.dk> To: Nate Lawson <nate@root.org> Cc: cvs-src@FreeBSD.org, src-committers@FreeBSD.org Subject: Re: cvs commit: src/sys/sys devicestat.h Message-ID: <2986.1047320558@critter.freebsd.dk> In-Reply-To: Your message of "Mon, 10 Mar 2003 10:13:36 PST." <Pine.BSF.4.21.0303101009420.93727-100000@root.org>
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In message <Pine.BSF.4.21.0303101009420.93727-100000@root.org>, Nate Lawson wri tes: Doesn't work: CPU0 (kernel) CPU1 (userland) increment seq start copy fiddle data end copy (copy is inconsistent) You need two sequence fields: CPU0 (kernel) CPU1 (userland) increment seq0 start copy fiddle data end copy increment seq1 (seq0 != seq1 indicates inconcistent data) Notice that to make it absolutely water-tight, the seq fields must be updated with appropriate write barriers and the order of the fields must be the opposite as the direction the copy is performed in. I may not think it worth going to that effort for io stats. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-src" in the body of the message
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